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Tetrakis
Selected AbstractsLead(II) Potentiometric Sensor Based on 1,4,8,11-Tetrathiacyclotetradecane Neutral Carrier and Lipophilic AdditivesELECTROANALYSIS, Issue 11 2008Mohamed Abstract A potentiometric sensor for lead(II) ions based on the use of 1,4,8,11-tetrathiacyclotetradecane (TTCTD) as a neutral ionophore and potassium tetrakis-(p -chlorophenyl)borate as a lipophilic additive in plasticized PVC membranes is developed. The sensor exhibits linear potentiometric response towards lead(II) ions over the concentration range of 1.0×10,5,1.0×10,2,mol L,1 with a Nernstian slope of 29.9,mV decade,1 and a lower limit of detection of 2.2×10,6,mol L,1 Pb(II) ions over the pH range of 3,6.5. Sensor membrane without a lipophilic additive displays poor response. The sensor shows high selectivity for Pb(II) over a wide variety of alkali, alkaline earth and transition metal ions. The sensor shows long life span, high reproducibility, fast response and long term stability. Validation of the method by measuring the lower limit of detection, lower limit of linear range, accuracy, precision and sensitivity reveals good performance characteristics of the proposed sensor. The developed sensor is successfully applied to direct determination of lead(II) in real samples. The sensor is also used as an indicator electrode for the potentiometric titration of Pb(II) with EDTA and potassium chromate. The results obtained agree fairly well with data obtained by AAS. [source] Amperometric Sensor for Heparin: Sensing Mechanism and Application in Human Blood Plasma AnalysisELECTROANALYSIS, Issue 13-14 2006Jan Langmaier Abstract Voltammetric measurements of heparin at a rotating glassy carbon (GC) electrode coated with a polyvinylchloride membrane are reported. A spin-coating technique is used to prepare thin membranes (20,40,,m) with a composition of 25% (w/w) PVC, 1,1,-dimethylferrocene as a reference electron donor for the GC|membrane interface, nitrophenyl octyl ether (o -NPOE) or bis(2-ethylhexyl) sebacate (DOS) as a plasticizer, and hexadecyltrimethylammonium tetrakis(4-chlorophenyl) borate (HTMATPBCl) or tridodecylmethylammonium tetrakis(4-chlorophenyl) borate (TDMATPBCl) as a background electrolyte. It is shown that the electrodes coated with either the HTMA+/o -NPOE (DOS) or TDMA+/o -NPOE (DOS) membrane provide a comparable amperometric response towards heparin (1,10,U mL,1) in the aqueous solution of 0.1,M LiCl. However, only the membranes formulated with TDMATPBCl can be used for an amperometric assay of heparin in human blood plasma with a detection limit of 0.2,U mL,1. Effects of membrane composition, heparin concentration, rotation speed and sweep rate on the voltammetric behavior of heparin provide some insight into the sensing mechanism. Theoretical analysis of the amperometric response is outlined, and the numeric simulation of the voltammetric behavior is presented. [source] Amperometry of Heparin Polyion Using a Rotating Disk Electrode Coated with a Plasticized PVC MembraneELECTROANALYSIS, Issue 2 2006Jan Langmaier Abstract Electrochemical method of detection of heparin polyion was developed based on voltammetry of heparin on a rotating glassy carbon (GC) electrode coated with a plasticized PVC membrane. The membrane was deposited on the GC disk by spin-coating technique using a mixture of solutions of PVC in tetrahydrofuran, and 1,1,-dimethylferrocene (DMFc) and hexadecyltrimethylammonium tetrakis(4-chlorophenyl)borate (HTMATPBCl) in o -nitrophenyl octyl ether. UV/vis reflection spectrometry was used to evaluate the membrane thickness, which exhibits a linear correlation with the membrane resistance measured by impedance spectroscopy. It is shown that this electrode can be used for amperometric or coulometric detection of heparin in aqueous samples of medically relevant concentrations (1,10,U mL,1), with a detection limit of 1.4,U mL,1. Evidence is provided indicating that the current determining step is the reversible adsorption of the ion-pair of heparin polyion with HTMA+ cation at the membrane/aqueous electrolyte interface, which is driven by oxidation of DMFc at the GC/membrane interface. [source] The Variable Binding Modes of Phenylbis(pyrid-2-ylmethyl)phosphane and Bis(pyrid-2-ylmethyl) Phenylphosphonite with AgI and CuIEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2009Fernando Hung-Low Abstract A series of new bridging phosphane and phosphonite structures forming three- and six-membered rings with the metal centers were synthesized and characterized. The resulting compounds of phenylbis(pyrid-2-ylmethyl)phosphane (1) with the silver(I) salts of trifluoroacetate (tfa,), tetrafluoroborate (BF4,), and trifluoromethanesulfonate (OTf,), and copper tetrakis(acetonitrile) hexafluorophosphate (PF6,) shows the flexibility of the ligand by displaying different coordination modes associated with the electronic and structural characteristics of the corresponding anion. Accordingly, ligand 1 in these complexes displays two different binding modes. With Agtfa and AgBF4 compounds 3 and 4 are obtained where the ligand chelates to two silver atoms that exhibit normalAg,Ag contacts in the range of 2.9 Å. When AgOTf or Cu(NCCH3)4PF6 are used, one molecule of 1 bridges the metal centers through a phosphorus atom while another is terminally bound. This induces short M,M distances of 2.6871 and 2.568 Å for 5 and 6, respectively. Similarly, the coordination behavior of the heterofunctional bis(pyrid-2-ylmethyl) phenylphosphonite ligand (2) is reported with Cu(NCCH3)4PF6 (7) and AgBF4 (8) to form two novel discrete molecules. In these complexes 2 coordinates through the P and N atoms, with the difference that in 7 the O atom of one of the carbinol arms is also bound to the Cu. Elemental analysis, variable-temperature multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and low-temperature luminescence studies were carried out to fully characterize the compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Characterization of Mixed Phthalocyaninato and meso -Tetrakis(4-chlorophenyl)porphyrinato Triple-Decker Complexes , Revealing the Origin of Their Electronic AbsorptionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004Xuan Sun Abstract Two series of mixed phthalocyaninato and porphyrinato rare earth(III) triple-decker complexes [M2(Pc)(TClPP)2] (1a,10a) and [M2(Pc)2(TClPP)] (1b,11b) [M = Y, La,Er except Ce and Pm; Pc = phthalocyaninate; TClPP = tetrakis(4-chlorophenyl)porphyrinate] have been prepared by treating the half-sandwich complexes [M(TClPP)(acac)] (acac = acetylacetonate), generated in situ from [M(acac)3]·nH2O and H2(TClPP), with Li2(Pc). All the triple-decker complexes have been characterized by a wide range of spectroscopic and electrochemical methods. The molecular structures of [M2(Pc)(TClPP)2] (M = Y, Ho) have also been determined, and show a symmetrical disposition of ligands, with two outer domed TClPP and one inner Pc rings. A systematic investigation of the optical and electrochemical data of these complexes has revealed the nature of the HOMO and LUMO, as well as the origin of the electronic absorptions of these triple-decker complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Photophysical and Energy-Transfer Properties of (Salen)zinc Complexes and Supramolecular AssembliesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003Kathryn E. Splan Abstract The absorption, emission, and energy-transfer properties of monomeric and supramolecular (salen)Zn complexes (square and rectangular assemblies) are reported. The monomeric complexes fluoresce in solution, displaying photophysical behavior similar to typical (porphyrin)zinc complexes. Rhenium coordination chemistry is used to assemble molecular rectangles and squares that largely retain the photophysical properties of the parent compounds. Host-guest assemblies obtained by binding a fifth (salen)Zn complex to a tetrakis(salen) square are capable of efficient salen-to-salen electronic energy transfer. Energy transfer flow through these systems can be manipulated by modification of the salen building-block structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis and Reactivity of 23 - tert -Butyl- and 23 -Phenyltetraarylazuliporphyrins: an Analysis of the Effect of Bulky Substituents on Oxidative Ring Contractions to Benzocarbaporphyrins,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2007Jessica A. El-Beck Abstract 6- tert -Butyl- and 6-phenylazulene reacted with pyrrole and benzaldehyde in a molar ratio of 1:3:4 in the presence of BF3·Et2O in chloroform, followed by oxidation with DDQ, to give 23 -substituted tetraphenylazuliporphyrins in 15,20,% yield. Slightly higher yields of the related meso -tetrakis(4-chlorophenyl)azuliporphyrins were obtained using 4-chlorobenzaldehyde. The presence of an electron-donating tert -butyl substituent increased the diatropic character of the azuliporphyrin system as determined by the proton NMR chemical shifts for the internal CH resonance, while intermediary results were noted for 23 -phenylazuliporphyrins. Addition of TFA afforded dications with increased aromatic ring currents, but electron-donating substituents (tBu,>,Ph) again produced a larger upfield shift for the internal CH signal due to stabilization of the tropylium character that is required so that the system can attain carbaporphyrin-type aromaticity. The substituted azuliporphyrins reacted with nickel(II) acetate or palladium(II) acetate to give the corresponding organometallic derivatives. In addition, oxidations with tBuOOH and KOH afforded benzocarbaporphyrin products in approximately 50,% yield. The presence of tert -butyl or phenyl substituents did not block these oxidative ring contraction processes, and the rate of reaction was slightly increased compared to 23 -unsubstituted azuliporphyrins. The major products were 22 - tert -butyl or phenyl-substituted benzocarbaporphyrins and minor products with an additional formyl substituent were also isolated. These products are consistent with an initial nucleophilic addition occurring at the position adjacent to the R group on the azulene ring. Detailed mechanisms are proposed to explain these observations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and Electrochemical Properties of Tetrasubstituted TetraphenylethenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2006Alina Schreivogel Abstract Tetrakis(4-acetoxyphenyl and 4-benzoyloxyphenyl)ethenes 1f and 1g were obtained by acylation of tetrakis(4-hydroxyphenyl)ethene 1b. Ullmann etherification of 4,4,-dihydroxybenzophenone 2b and subsequent McMurry coupling yielded tetrakis(phenoxyphenyl)ethene 1i. The tetrakis(acetamidophenyl)ethene 1h was prepared in three steps from tetraphenylethene 1c by nitration, Raney-Ni reduction and subsequent acetylation. Alternatively, trifluoroacetamide 1j, 2-methylhexanamide 1k and 2,4-dimethylbenzamide 1l, with less tendency to form 2D hydrogen bonding networks and thus increased solubility as compared to 1h, were prepared by acylation of 4,4,-diaminobenzophenone 2a and subsequent McMurry coupling. Compounds 1f,l were investigated by cyclic voltammetry. While the phenyl ether derivative 1i displays single-electron processes during oxidation, a two-electron process was discovered for trifluoroacetamide 1j as was also supposed for the esters 1f and 1g. In addition, comproportionation constants were shown to be dependent on the solvent. In situ IR spectroelectrochemistry provided evidence for quinoidal type substructures in the dioxidized forms of tetraphenylethenes 1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Coordination chemistry of iron(III),porphyrin,antibody complexesFEBS JOURNAL, Issue 2 2002Influence on the peroxidase activity of the axial coordination of an imidazole on the iron atom An artificial peroxidase-like hemoprotein has been obtained by associating a monoclonal antibody, 13G10, and its iron(III),,,,,,,,- meso -tetrakis(ortho -carboxyphenyl)porphyrin [Fe(ToCPP)] hapten. In this antibody, about two-thirds of the porphyrin moiety is inserted in the binding site, its ortho -COOH substituents being recognized by amino-acids of the protein, and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O,O bond of H2O2, but no amino-acid residue is acting as an axial ligand of the iron. We here show that the iron of 13G10,Fe(ToCPP) is able to bind, like that of free Fe(ToCPP), two small ligands such as CN,, but only one imidazole ligand, in contrast to to the iron(III) of,Fe(ToCPP) that binds two. This phenomenon is general for a series of monosubstituted imidazoles, the 2- and 4-alkyl-substituted imidazoles being the best ligands, in agreement with the hydrophobic character of the antibody binding site. Complexes of antibody 13G10 with less hindered iron(III),tetraarylporphyrins bearing only one [Fe(MoCPP)] or two meso-[ortho -carboxyphenyl] substituents [Fe(DoCPP)] also bind only one imidazole. Finally, peroxidase activity studies show that imidazole inhibits the peroxidase activity of 13G10,Fe(ToCPP) whereas it increases that of 13G10,Fe(DoCPP). This could be interpreted by the binding of the imidazole ligand on the iron atom which probably occurs in the case of 13G10,Fe(ToCPP) on the less hindered face of the porphyrin, close to the catalytic COOH residue, whereas in the case of 13G10,Fe(DoCPP) it can occur on the other face of the porphyrin. The 13G10,Fe(DoCPP),imidazole complex thus constitutes a nice artificial peroxidase-like hemoprotein, with the axial imidazole ligand of the iron mimicking the proximal histidine of peroxidases and a COOH side chain of the antibody acting as a general acid-base catalyst like the distal histidine of peroxidases does. [source] Enhanced-Light-Harvesting Amphiphilic Ruthenium Dye for Efficient Solid-State Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Mingkui Wang Abstract A ruthenium sensitizer (coded C101, NaRu (4,4,-bis(5-hexylthiophen-2-yl)-2,2,-bipyridine) (4-carboxylic acid-4,-caboxylate-2,2,-bipyridine) (NCS)2) containing a hexylthiophene-conjugated bipyridyl group as an ancillary ligand is presented for use in solid-state dye-sensitized solar cells (SSDSCs). The high molar-extinction coefficient of this dye is advantageous compared to the widely used Z907 dye, (NaRu (4-carboxylic acid-4,-carboxylate) (4,4,-dinonyl-2,2,-bipyridine) (NCS)2). In combination with an organic hole-transporting material (spiro-MeOTAD, 2,2,,7,7,-tetrakis-(N,N -di- p -methoxyphenylamine) 9, 9,-spirobifluorene), the C101 sensitizer exhibits an excellent power-conversion efficiency of 4.5% under AM 1.5 solar (100 mW cm,2) irradiation in a SSDSC. From electronic-absorption, transient-photovoltage-decay, and impedance measurements it is inferred that extending the ,-conjugation of spectator ligands induces an enhanced light harvesting and retards the charge recombination, thus favoring the photovoltaic performance of a SSDSC. [source] PbS and CdS Quantum Dot-Sensitized Solid-State Solar Cells: "Old Concepts, New Results"ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009HyoJoong Lee Abstract Lead sulfide (PbS) and cadmium sulfide (CdS) quantum dots (QDs) are prepared over mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) process. These QDs are exploited as a sensitizer in solid-state solar cells with 2,2,,7,7,-tetrakis(N,N -di- p -methoxyphenylamine)-9,9,-spirobifluorene (spiro-OMeTAD) as a hole conductor. High-resolution transmission electron microscopy (TEM) images reveal that PbS QDs of around 3,nm in size are distributed homogeneously over the TiO2 surface and are well separated from each other if prepared under common SILAR deposition conditions. The pore size of the TiO2 films and the deposition medium are found to be very critical in determining the overall performance of the solid-state QD cells. By incorporating promising inorganic QDs (PbS) and an organic hole conductor spiro-OMeTAD into the solid-state cells, it is possible to attain an efficiency of over 1% for PbS-sensitized solid-state cells after some optimizations. The optimized deposition cycle of the SILAR process for PbS QDs has also been confirmed by transient spectroscopic studies on the hole generation of spiro-OMeTAD. In addition, it is established that the PbS QD layer plays a role in mediating the interfacial recombination between the spiro-OMeTAD+ cation and the TiO2 conduction band electron, and that the lifetime of these species can change by around 2 orders of magnitude by varying the number of SILAR cycles used. When a near infrared (NIR)-absorbing zinc carboxyphthalocyanine dye (TT1) is added on top of the PbS-sensitized electrode to obtain a panchromatic response, two signals from each component are observed, which results in an improved efficiency. In particular, when a CdS-sensitized electrode is first prepared, and then co-sensitized with a squarine dye (SQ1), the resulting color change is clearly an addition of each component and the overall efficiencies are also added in a more synergistic way than those in PbS/TT1-modified cells because of favorable charge-transfer energetics. [source] Pore-Filling of Spiro-OMeTAD in Solid-State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 15 2009I-Kang Ding Abstract In this paper, the pore filling of spiro-OMeTAD (2,2,,7,7,-tetrakis-(N,N -di- p -methoxyphenylamine)9,9,-spirobifluorene) in mesoporous TiO2 films is quantified for the first time using XPS depth profiling and UV,Vis absorption spectroscopy. It is shown that spiro-OMeTAD can penetrate the entire depth of the film, and its concentration is constant throughout the film. We determine that in a 2.5-µm-thick film, the volume of the pores is 60,65% filled. The pores become less filled when thicker films are used. Such filling fraction is much higher than the solution concentration because the excess solution on top of the film can act as a reservoir during the spin coating process. Lastly, we demonstrate that by using a lower spin coating speed and higher spiro-OMeTAD solution concentration, we can increase the filling fraction and consequently the efficiency of the device. [source] Charge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based SensitizerADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Henry J. Snaith Abstract An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2,,7,7,-tetrakis(N,N -di- p -methoxypheny-amine)-9,9,-spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10,mW cm,2. However, a considerable nonlinearity in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100,mW cm,2. The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8,×,1017,cm,3 under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions. [source] Nanosensor Design Packages: A Smart and Compact Development for Metal Ions Sensing Responses,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007A. El-Safty Abstract With recent advances in mesostructured materials and nanotechnologies, new methods are emerging to design optical sensors and biosensors, and to develop highly sensitive solid sensors. Here, highly sensitive, low cost, simple nanosensor designs for naked-eye detection of toxic metal ions are successfully developed by the immobilization of commercially available ,,,,,,,-tetrakis(1-methylpyridinium-4-yl)porphine p -toluenesulfonate (TMPyP) and diphenylcarbazide (DPC), and chemically synthesized 4- n -dodecyl-6-(2-thiazolylazo) resorcinol (DTAR) and 4- n -dodecyl-6-(2-pyridylazo) phenol (DPAP) chromophore molecules into spherical nanosized cavities and surfaces. A rational strategy was crucial to develop optical nanosensors that can be used to control accurate recognition and signaling abilities of analyte species for ion-sensing purposes. This is the first reported evidence of the significant key factors of the development of receptors as ,indicator dyes' and surface-confinement materials as ,carriers' to broadening the applicability of optical chemical sensors for selective discrimination of trace levels of toxic analytes. In all the nanosensor design techniques presented here, a dense pattern of immobilized hydrophobic ,neutral' and hydrophilic ,charged' chromophores with intrinsic mobility, as a result of extremely robust constructed sequences on nanoscale structures, is a key to enhancing the sensing functionality of optical nanosensors. These nanosensor designs can be used as cage probe sinks with reliable control, for the first time, over the colorimetric recognition of cadmium ions to low levels of concentration in the range of 10,9 to 10,10M. Optimization of control sensing conditions is established to achieve enhanced signal response and color intensities. These chemical nanosensors are reversible and have the potential to serve effectively in on-site field analysis of environmental samples, which eliminates the necessity for instrument-dependent analysis. Moreover, these new classes of optical cage sensors exhibit long-term stability of signaling and recognition functionalities that in general provide extraordinary sensitivity, selectivity, reusability, and fast kinetic detection and quantification of various deleterious metal ions in our environment. [source] Fabrication of Organized Porphyrin-Nanotube-Attached Heat-Sensitive Polyelectrolyte Capsules,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006S. Sadasivan Abstract A facile method of connecting fluorescent meso -tetrakis(4-sulfonatophenyl)porphine tetranion nanotubes to polyelectrolyte capsules is developed. Heat-sensitive robust polyelectrolyte capsules consisting of poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) multilayers have been fabricated using the conventional layer-by-layer technique. Supramolecular aggregation of porphyrin monomers to nanotubes is induced in the microenvironment of the capsules by sequential addition of salt and acid. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy images reveal satellite-like structures consisting of a central capsule core with porphyrin nanotubes emerging radially from the capsule walls. The growth and the distribution of the porphyrin units have been monitored by UV-vis spectroscopy, fluorescence spectroscopy, and confocal laser scanning microscopy. Changing the temperature alters the dimensions and the arrangement of the nanotubes on the capsule walls. Such an attachment of porphyrin tubes onto robust functional capsules should help in developing an artificial light-harvesting system. [source] Tetrakis(trimethysilyl)hypophosphate P2O2(OTMS)4: Synthesis, reactivity and application as flame retardantHETEROATOM CHEMISTRY, Issue 7 2007Catherine Ruflin The preparation of tetrakis(trimethy- silyl)hypophosphate, P2O2(OTMS)4 (TMS = SiMe3), which is easily obtained from cheap starting materials, is reported. Reaction with protic substrates (H2O, alcohols) proceeds under stepwise cleavage of silylethers, ROTMS, and formation of hypophosphoric acid, P2O2(OH)4. Amines in the presence of molecular sieves lead to desilylation and formation of ammonium salts of the [P2O2(OTMS)2(O,)2] dianion. On cotton fabrics, P2O2(OTMS)4 hydrolyzes to give P2O2(OH)4 within about 1 h when exposed to air, and this compound acts as an efficient flame retardant (limiting oxygen index >26%) even at low loadings (P content <3%). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:721,731, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20373 [source] Organotins-promoted peroxidation of unsaturated fatty acids: A new antioxidative scavenger for promotersHETEROATOM CHEMISTRY, Issue 6 2006Elena R. Milaeva The organotin compounds RnSnX4- n are promoters of lipids peroxidation. The influence of (CH3)2SnCl2, (C2H5)2SnCl2, and SnCl2 upon the radical chain oxidation of oleic acid as model substrate R,H for lipid peroxidation in the simultaneous presence of porphyrins (free bases of meso -tetrakis(3,5-di- tert -butyl-4-hydroxyphenyl)porphyrin (R,4PH2) and of meso -tetraphenylporphyrin (TPPH2)) has been studied. The monitoring of the unsaturated acid peroxidation level has been performed by the determination of the total concentration of isomeric hydroperoxides as well as of the thiobarbituric acid reactive substances, as markers of carbonyl compounds formation following the hydroperoxides decomposition. The organotin compounds demonstrate prooxidative activity. The promoting effect of these compounds decreases in the presence of TPPH2. The free-base porphyrin R,4PH2, containing the antioxidative phenolic moieties (2,6-di- tert -butylphenol), demonstrates the acute inhibitory effect upon the acid's peroxidation. The analogous results have been achieved when compared with the influence of CH3HgI and HgCl2 upon the acids peroxidation of oleic acid in the presence of porphyrins. This fact points out that meso- tetrakis(3,5-di- tert -butyl-4-hydroxyphenyl)porphyrin shows the activities of both the antioxidant and of the scavenger for metals and might be used as a new antioxidative scavenger preventing lipids peroxidation. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:475,480, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20269 [source] Catalytic Asymmetric Mannich Reaction of Glycine Derivatives with N -Tosylimines using Copper(I)/TF-BiphamPhos ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Gang Liang Abstract The direct asymmetric Mannich reaction of glycine Schiff bases with N -tosylimines has been developed with the tetrakis(acetonitrile)copper(I) tetrafluoroborate [Cu(CH3CN)4BF4]/TF-BiphamPhos complex. This catalytic system performs well over a broad range of substrates, furnishing anti -adducts of various ,,,-diamino acid esters in good yields with up to 94:6 diastereoselectivity and 97% enantioselectivity. [source] Highly Efficient and Enantioselective Iridium-Catalyzed Asymmetric Hydrogenation of N -AryliminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Wei Li Abstract A catalytic method employing the cationic iridium-(Sc,Rp)-DuanPhos [(1R,1,R,2S,2,S)-2,2,-di- tert -butyl-2,2,,3,3, -tetrahydro-1H,1,H -1,1,-biisophosphindole] complex and BARF {tetrakis[3,5-bis(trifluoromethyl)phenyl]borate} counterion effectively catalyzes the enantioselective hydrogenation of acyclic N -arylimines with high turnover numbers (up to 10,000 TON) and excellent enantioselectivities (up to 98% ee), achieving the practical synthesis of chiral secondary amines. [source] Immobilization of Porphyrinatocopper Nanoparticles onto Activated Multi-Walled Carbon Nanotubes and a Study of its Catalytic Activity as an Efficient Heterogeneous Catalyst for a Click Approach to the Three-Component Synthesis of 1,2,3-Triazoles in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Hashem Sharghi Abstract An efficient, regioselective, one-pot and two-step synthesis of ,-hydroxy 1,4-disubstituted 1,2,3-triazoles from a wide range of non-activated terminal alkynes and epoxides and sodium azide by way of a three-component click reaction using a catalytic amount of [meso -tetrakis(o -chlorophenyl)porphyrinato]copper(II) (5,mol%) in excellent isolated yields is described. The reactions were performed in water as a green solvent at ambient temperature without any additives. By performing two reaction steps in one pot and purifying only at the final step, this procedure excludes any interim purification of in situ generated organic azide intermediates, which significantly improves the overall yield and reduces the reaction time. To benefit from the recovery and reuse of the catalyst, a new heterogeneous catalyst was prepared by simple and successful impregnation of the catalyst onto activated multi-walled carbon nanotubes (AMWCNT). The heterogeneous catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic forced microscopy (AFM), and thermogravimetric (TG) analysis to estimate the amount of nitrogen adsorption, and Raman and FT-IR spectroscopy. Leaching experiments after ten successive cycles showed that the catalyst is most strongly anchored to the AMWCNT support. Mechanistically, porphyrinatocopper catalyzes each step of the reaction in different ways as a bifunctional catalyst including epoxide ring opening by azide delivery to epoxide, forming in situ generated 2-azido alcohols followed by activation of the CC triple bond of the starting terminal alkynes by forming a porphyrinatocopper-acetylide intermediate and thereby promoting the [3+2]-cycloaddition reaction as the key step to form the triazole framework. [source] Diethylzinc: A Simple and Efficient Catalyst for the Swift Hydroamination at Room TemperatureADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Jens-Wolfgang Pissarek Abstract Diethylzinc and dimethylanilinium tetrakis(pentafluorophenyl)borate were found to catalyze hydroaminations at room temperature in high efficiency and very short reaction times. The reactivity of the proposed cationic zinc species, which is assumed to catalyze the reaction, strongly depends on the coordinative abilities of the counterion. [source] Conventional Tetrakis(triphenylphosphine)palladium-Copper(I) Iodide-Catalyzed Sonogashira Coupling of Free and BOC- Protected Propargylic Amines "On Water"ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Bartomeu Soberats Abstract Alkynylation of aryl iodides with propargylic amines has been achieved by means of a Sonogashira coupling using "on water" methods. The use of less than 0.2,mol% of tetrakis(triphenylphosphine)palladium [Pd(PPh3)4] and 1.5,mol% copper(I) iodide [CuI] in the presence of diisopropylethylamine (DIPEA) allows the coupling to proceed at 95,°C yielding moderate to good yields of mono-, bis-, and tris-aminoalkynylbenzene derivatives. [source] Regioselective Palladium(0)-Catalyzed Cross-Coupling Reactions and Metal-Halide Exchange Reactions of Tetrabromothiophene: Optimization, Scope and LimitationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009ng Thanh Tùng Abstract The Suzuki reaction of tetrabromothiophene with arylboronic acids provides a regioselective approach to various 5-aryl-2,3,4-tribromothiophenes, symmetrical 2,5-diaryl-3,4-dibromothiophenes, and tetraarylthiophenes. Unsymmetrical 2,5-diaryl-3,4-dibromothiophenes are prepared by Suzuki reaction of 5-aryl-2,3,4-tribromothiophenes. Tetraarylthiophenes containing two different types of aryl groups are obtained by Suzuki reactions of 2,5-diaryl-3,4-dibromothiophenes. During the optimization of the conditions of each individual reaction, the solvent, the catalyst and the temperature play an important role. In several cases, classical conditions [use of tetrakis(triphenylphosphane)palladium(0), Pd(PPh3)4, as the catalyst] gave excellent yields. The yields of those transformations which failed or proceeded sluggishly could be significantly improved by application of a new biarylmonophosphine ligand developed by Buchwald and co-workers. Regioselective metal-halide exchange reactions of tetrabromothiophene provide a convenient approach to various 2,5-disubstituted 3,4-dibromothiophenes. 5-Alkyl-2-trimethylsilyl-3,4-dibromothiophenes could be prepared in one pot by sequential addition of trimethylchlorosilane and alkyl bromides. The reaction of tetrabromothiophene with methyl chloroformate and subsequent Suzuki reactions afforded 3,4-diaryl-2,5-bis(methoxycarbonyl)thiophenes. [source] Reduction of Alkyl Halides by Triethylsilane Based on a Cationic Iridium Bis(phosphinite) Pincer Catalyst: Scope, Selectivity and MechanismADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Jian Yang Abstract A highly efficient procedure for the reduction of a broad range of alkyl halides by triethylsilane based on a cationic iridium bis(phosphinite) pincer catalyst has been discovered and developed. This reduction chemistry is chemoselective and has unique selectivities compared with conventional radical-based processes and the aluminum trichloride/triethylsilane (AlCl3/Et3SiH) and triphenylmethyl tetrakis[pentafluorophenyl]borate/triethylsilane {[Ph3C] [B(C6F5)4]/Et3SiH} systems. Reductions use three equivalents of triethylsilane relative to the halide and can be carried out with very low catalyst loadings and in a solvent-free manner, which may provide an environmentally attractive and safe alternative to many currently practiced methods for reduction of alkyl halides. Mechanistic studies reveal a unique catalytic cycle. The cationic iridium hydride 2,6-bis[di-(tert -butyl)phosphinyloxy)phenyl(hydrido)iridium, (POCOP)IrH+ {POCOP= 2,6-[OP(t- Bu)2]2C6H3} binds and activates the silane. This complex serves as a potent silylating reagent to generate silyl halonium ions, Et3SiXR+, which are reduced by the neutral iridium dihydride to yield alkane product and regenerate the cationic (POCOP)IrH+, thus closing the catalytic cycle. All key intermediates have been identified by in situ NMR monitoring and kinetic studies have been completed. An application of this reduction system to the catalytic hydrodehalogenation of a metal chloride complex is also described. [source] Air-Stable and Highly Active Dendritic Phosphine Oxide- Stabilized Palladium Nanoparticles: Preparation, Characterization and Applications in the Carbon-Carbon Bond Formation and Hydrogenation ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2008Lei Wu Abstract Dendrimer-stabilized palladium nanoparticles were formed in the reduction of palldium bis(acetylacetonate) [Pd(acac)2] in the presence of phosphine dendrimer ligands using hydrogen in tetrahydrofuran. The resulting Pd nanoparticles were characterized by TEM, 31P,NMR and 31P MAS NMR. The results indicated that the dendritic phosphine ligands were oxidized to phosphine oxides. These dendrimer-stabilized Pd nanoparticles were demonstrated to be efficient catalysts for Suzuki and Stille coupling reactions and hydrogenations. The dendritic wedges served as a stabilizer for keeping the nanoparticles from aggregating, and as a vehicle for facilitating the separation and/or the recycling of the Pd catalyst. In the case of the Suzuki coupling reaction, these Pd nanoparticles exhibited high catalytic efficiency (TON up to 65,000) and air stability as compared with the commonly used homogeneous catalyst tetrakis(triphenylphosphine)palladium [Pd(PPh3)4]. In addition, the results obtained from the bulky dendritic substrate suggest that the Pd nanoparticles might act as reservoir of catalytically active species, and that the reaction is actually catalyzed by the soluble Pd(0) and/or Pd(II) species leached from the nanoparticle surface. [source] Homogeneous Hydrogenation of Tri- and Tetrasubstituted Olefins: Comparison of Iridium-Phospinooxazoline [Ir-PHOX] Complexes and Crabtree Catalysts with Hexafluorophosphate (PF6) and Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF) as CounterionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2008Bettina Wüstenberg Abstract Four iridium complexes with achiral phosphino-oxazoline (PHOX) ligands were readily prepared in two steps starting from commercially available phenyloxazolines. The air-stable complexes with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF) as counterion showed high reactivity in the hydrogenation of a range of tri- and tetrasubstituted olefins. The best results were obtained with an iridium complex (11) derived from a dicyclohexylphosphino-oxazoline ligand bearing no additional substituents in the oxazoline ring. With several substrates, which gave only low conversion with the Crabtree catalyst, [Ir(Py)(PCy3)(COD)]PF6, full conversion was observed. The productivity of the Crabtree catalyst could be strongly increased by replacing the hexafluorophosphate anion with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. In one case, in the hydrogenation of a tetraalkyl-substituted CC bond, [Ir(Py)(PCy3)(COD)]BArF gave higher conversion than catalyst 11. However, with several other substrates complex 11 proved to be superior. [source] Formulation and characterization of radio-opaque conjugated in situ gelling materials,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010Brandon Blakely Abstract X-ray visibility is an integral design component of in situ gelling embolization systems for neurovascular treatment. The goals of this project included the synthesis and characterization of a unique intrinsically radio-opaque in situ gelling material for neurovascular embolization. The gels formed using Michael-Type Addition between pentaerythritol tetrakis 3-mercaptopropionate (QT) thiols and poly(propylene glycol) diacrylate (PPODA) with the addition of the new material Iodobenzoyl poly(ethylene glycol) acrylate (IPEGA), a radio-opaque agent, synthesized successfully as confirmed with 1H NMR. The PPODA and IPEGA were mixed using a syringe coupler with QT and buffer at pH 11 for 90 seconds. Gel mixes were weighed to provide equal molar thiols and acrylate groups, changing the present acrylate-bearing compounds wt % ratios from 100 PPODA: 0 IPEGA, 90:10, 80:20, 70:30, 60:40, 50:50, and 0:100. Formulations with 10% and above of IPEGA were X-ray visible. Rheology showed that increasing the amount of IPEGA decreased the storage. Kinetic FT-IR studies indicate that the amphiphilic nature of the PEG backbone increased the reaction rate of the phase segregated reactants. Second order reaction constant modeling showed a change in initial reaction rate from 0.0029 to 0.0187 (M sec),1 from the 10% to 50% IPEGA formulations respectively. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Zinc regulates the ability of Cdc25C to activate MPF/cdk1JOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2007Lu Sun Zn2+ is an essential micronutrient for the growth and development of multicellular organisms, as Zn2+ deficiencies lead to growth retardation and congenital malformations (Vallee, BL, Falchuk, KH. 1993. Physiol Rev., 73:79,118). At the cellular level Zn2+ depravation results in proliferation defects in many cell types (Vallee, BL, Falchuk, KH. 1993. Physiol Rev., 73:79,118), however the molecular pathways involved remain poorly defined. Here we show that the transition metal chelator TPEN (N,N,N,,N,-tetrakis(2-pyridylmethyl) ethylene diamine) blocks the G2/M transition of the meiotic cell cycle by inhibiting Cdc25C-cdk1 activation. ICP-MS analyses reveal that Cdc25C is a Zn2+ -binding metalloprotein, and that TPEN effectively strips Zn2+ away from the enzyme. Interestingly, although apo-Cdc25C (Zn2+ -deficient) remains fully catalytically active, it is compromised in its ability to dephosphorylate and activate MPF/cdk1. Thus, Zn2+ is an important regulator of Cdc25C function in vivo. Because of the conserved essential role of the Cdc25C-cdk1 module in the eukaryotic cell cycle, these studies provide fundamental insights into cell cycle regulation. J. Cell. Physiol. 213: 98,104, 2007. © 2007 Wiley-Liss, Inc. [source] A non-peptide radioiodinated high affinity melanocortin-4 receptor ligandJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 11 2003Felikss Mutulis Abstract 4-Cyclohexyl-4-[(1,2,4-triazol-1-yl)methyl]piperidine was introduced into stepwise peptide synthesis procedures using Boc chemistry and derivatives of D -4-iodophenylalanine and D -1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid. A halogen replacement analogue (I-Mex2) of a known high affinity melanocortin-4 receptor selective compound resulted. It showed a subnanomolar affinity when evaluated on the melanocortin-4 receptor in competition with the , -MSH peptide analogue 125I-NDP-MSH. By treatment with hexamethylditin and tetrakis(triphenylphosphine) palladium I-Mex2 was converted to the corresponding trimethylstannyl derivative. In the next step, Na125I was oxidized by an iodobead. Iododestannylation proceeded in the presence of 1 M phosphate buffer, pH 2.5, and the radio-active derivative 125I-Mex2 formed was separated by HPLC at 40% radiochemical yield. Preliminary investigation showed that 125I-Mex2 is useful as a radioligand for melanocortin-4 receptor binding studies. Copyright © 2003 John Wiley & Sons, Ltd. [source] A new practical tritium labelling procedure using sodium borotritide and tetrakis(triphenylphosphine)palladium(0)JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 14 2001Tohru Nagasaki Abstract A simple, mild and versatile new tritium (3H) labelling method on a micro scale using sodium borotritide (NaB3H4) and a transition,metal complex catalyst is described. 3H-labelled compounds were prepared effectively by 3H hydrogenolysis of appendant functional groups in target compounds. The appendant functional group such as bromo, iodo or sulfonate in various target compounds can be replaced by tritium (3H) in moderate yields. The new method was established by optimization of the reaction conditions and examination of its applicability using four types of model substrates in tracer runs. Then, various drug candidates and ligands for drug discovery were labelled with tritium on a micro scale. The specific radioactivity of the 3H-labelled compounds used for the studies on receptor binding ranged from 12 to 20 Ci/mmol. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||